1. Field of the Invention
The invention relates to an apparatus for analyzing a contaminated surface comprising a transfer device having a porous disk-shaped medium and comprising an analytical device. The invention further relates to a method for analyzing a contaminated surface using the aforementioned apparatus.
2. Description of the Related Art
Various analytical methods have been established in the analysis of contaminated surfaces.
U.S. Pat. No. 5,232,838 discloses a mount composed of a self-supporting support layer to which a water-soluble adhesive layer is applied. A water-soluble “instant” powder which forms a culture medium for microorganisms upon contact with water is sprinkled in turn onto the adhesive layer. This layered structure is covered by a peelable protective film. After peeling off the protective film, the adhesive layer containing the “instant” powder can be pressed onto a contaminated surface in order to bring the microbes from the surface onto the mount. Subsequently, the affixed “instant” powder is contacted with water in order to initiate the culturing of the microorganisms by the culture medium formed from the “instant” powder.
GB 2 019 434 A discloses an adhesive film in which a porous supporting layer composed of cellulose ester derivatives is coated with an adhesive layer composed of, for example, polyvinylpyrrolidone, polyethylene glycol or polyvinyl methyl ether. The supporting layer can be mechanically stabilized on its side facing away from the adhesive layer by a porous peelable foam layer which facilitates the pressing of the adhesive film onto a microbe-contaminated surface. After removal of the adhesive film from the contaminated surface, the film is placed down on a culture medium with the side facing away from the adhesive layer in order to culture the captured microorganisms.
EP 0 816 513 B1 discloses adhesive films consisting of a water-permeable, but microbe-impermeable, membrane to which an adhesive layer composed of a water-soluble polymer is applied, said adhesive layer being able to fix microbes. The membrane can optionally be applied to a supporting layer. Using these films, microorganisms can be removed from contaminated surfaces by means of the adhesive layer. The film, which can be present in the form of a filter circle, can then be introduced into a filtration unit and be contacted with an aqueous solution containing a staining (chromogenic) substance for the microorganisms. The water-soluble polymer dissolves and passes, with the aqueous solution, the membrane, whereas the microbes are retained on the membrane surface on which the adhesive layer was once situated in order to be subsequently analyzed.
Also widespread is the use of special swabs. These are rods comprising, at one end, a porous thickening with which the surfaces to be tested are intensively rubbed and which are then washed out in subsequent analytical steps in order to test the adherent contamination.
Said swabs are used for all types of surface analyses, whether it be for (bio)chemical methods, for example for DNA analysis, or else for microbiological tests for determining surface contamination.
For the quantitative and semiquantitative determination of surface contamination, it is necessary to detach adherent microorganisms from the swab as quantitatively as possible in order not to falsify the subsequent further test steps. Direct transfer into a culture medium with subsequent testing for growth after incubation is adequate only when checking the sterility of a surface.
The transfer step is never completely achieved and this means that quantitative and semiquantitative analyses using such swabs are difficult to validate because, firstly, contamination as described above is not detachable from the swabs in a reliably quantitative manner and, secondly, the size of the sample area is not quantitatively defined by rubbing with swabs.
Therefore, contact agar plates, which allow a direct evaluation of pathogen counts after appropriate incubation, are primarily used for the quantitative determination of surface contamination.
Instead of swabs, cellulose nitrate membranes can also be used for the quantitative determination of surface contamination, since the electrostatically charged membrane surface pulls off pathogens from the surface to be tested and binds them to the membrane surface structure. These membranes can then be transferred to an agar culture medium and can be quantitatively evaluated after incubation analogously to the method using contact agar plates.
M. Pitzurra et al., Hygiene & Medizin, 22 (2) 1997, 77-92, mhp-Verlag, disclose said method using cellulose nitrate membranes compared to methods using contact agar plates or swabs and to a wash-off method.
The method disclosed by M. Pitzurra et al. has the advantage that the surfaces are not soiled by moist growth or culture medium, as occurs when using contact agar plates, and that the method, compared to swabs, allows direct quantitative evaluation.
In addition, for the area of filtration-based pathogen count determination, a plurality of quick methods are available for liquids, and so the membranes can be directly introduced to these methods after sampling.
Despite the aforementioned advantages with respect to swabs and contact agar plates, said method tested by Pitzurra et al. has so far not been established, since the required sterile handling of the fragile membranes, which typically have a diameter of about 50 mm and a thickness of 100-200 μm, is very laborious and, in terms of the method, not robust. Thus, sampling is very time-consuming and requires attention when removing the membrane from the surface to be analyzed and when further treating the membrane. Also, this method requires the manipulation of the fragile membrane with further technical aids, for example tweezers. The results can be compromised by contamination. These disadvantages also hamper, in particular, reproducible sampling, as required by GLP (“Good Laboratory Practice”) and GMP (“Good Manufacturing Practice”) regulations for the pharmaceutical industry.
WO 2008/113444 A1 discloses a culture media unit for removing a filter from a filter support device of a filtration apparatus. The culture media unit comprises a bottom part filled with culture medium and a lid.
The lid has a fixing edge which projects into the bottom part and which is bindable to an edge of the filter via an adhesive bond with the filter in order to remove the filter from the filtration apparatus. Said lid makes it possible, without using tweezers or other aids, to transfer the filter from the filter support device into the culture media unit solely by means of the fixing edge of the lid.
The described unit is suitable for microbiological testing of liquid samples after preceding filtration.
DE 20 2009 016 410 U1 discloses a transfer unit for microbiological analysis for accommodating a porous, disk-shaped medium, which transfer unit can remove the medium, by means of a fixing edge, from a first treatment apparatus via the edge of the medium and which transfer unit has an opening which is closable by a removable lid and via which it is possible to carry out subsequent treatment of the medium in a further treatment apparatus.
JP 2008/193919 A discloses a culturing container composed of two book cover-shaped parts joined to one another via a hinge joint, for the analysis of bacterial contamination on surfaces. The first part, which acts as the lid of the culturing container, has a circular projection with a planar adhesive coating. The second part, which acts as a bottom part of the culturing container, has a bowl-shaped recess which is fillable with a culture medium for bacteria. The adhesive-coated projection of the lid can be pressed onto a bacterially contaminated surface, and the bacteria are fixed on the projection by means of the adhesive coating. Subsequently, the lid is folded onto the bottom part by means of the hinge joint and the bacteria fixed on the projection contact the culture medium in the bottom part via uniform contact between the projection and the surface of the culture medium.
JP 2007/135542 A discloses a culturing container similar to the aforementioned culturing container of JP 2008/193919 A, having a separate lid and a separate bottom part containing a culture medium for bacteria to be analyzed. The lid, which is removable from the bottom part, has a circular adhesive coating on its inner lid wall, which is facing the culture medium. Bacteria can be removed from a contaminated surface by means of said adhesive coating and, after their fixation on the adhesive layer, the lid is put over the bottom part such that the bacteria-containing adhesive layer of the lid uniformly adheres to the culture media surface in the bottom part.
The two aforementioned apparatuses, which have proved their worth in principle, are not suitable for carrying out an analysis of contaminated surfaces using porous disk-shaped media, for example membrane filters, since the analysis of the bacteria to be tested can be interfered with in an undesired manner by the adhesive from the adhesive coating that is fixing the bacteria.
It is an object of the present invention to provide an apparatus and a method with which it is possible to quantitatively analyze a contaminated surface using mechanically unstable or fragile porous disk-shaped media without using structurally complex systems and without using further technical aids and without breaking or altering the surface to be analyzed of the disk-shaped media after removal from the contaminated surface and before carrying out the analysis.